High-dispersity tungsten oxide ink as well as preparation method and application thereof

Abstract

The invention discloses high-dispersity tungsten oxide ink as well as a preparation method and application thereof in electrochromism, and belongs to the technical field of electrochromic films. The preparation method comprises the following steps: (1) preparing additive-free high-dispersity tungsten oxide (WO3-x) ink through an alcohol solvothermal method; (2) coating the uniformly dispersed ink on a substrate through a spraying, spin coating or pulling method to form an electrochromic film; and (3) annealing the prepared film so as to improve the electrochromism performance of the film. The preparation method disclosed by the invention is simple in process and convenient to operate, and the prepared tungsten oxide ink has excellent dispersity under the condition of no additive, is suitable for various film preparation processes such as ink-jet printing, spin coating, spraying and the like, has good large-scale production capacity and is suitable for industrial production. And particularly, wide application prospects are shown in the fields of electrochromic display devices, intelligent windows and the like.

Description

Technical Field

[0001] The present invention relates to the field of nanomaterials and electrochromics, and particularly to a highly dispersible tungsten oxide (WO 3-x , 0 < x < 3) ink and its preparation method and application. Background Art

[0002] Electrochromic technology is widely used in fields such as smart windows and building energy conservation, automotive rearview mirrors and sun visors, display devices, wearable devices, military camouflage, and artistic decoration due to its characteristic of reversibly changing the optical properties of materials under an applied voltage. Compared with organic electrochromic materials, inorganic transition metal oxide materials have received extensive attention due to their good reversibility and electrochemical stability.

[0003] Among them, tungsten oxide, as an inorganic electrochromic material with broad development prospects, especially non-stoichiometric tungsten oxide (WO 3-x ), the local surface plasmon resonance (LSPR) effect in the near-infrared range of its nanocrystals can further improve the electrochromic performance of the material. Traditional electrochromic thin films usually adopt vacuum coating methods, such as magnetron sputtering or electron beam ion beam evaporation. These methods have problems such as complex processes and high costs, which limit their large-scale application. The electrochromic thin films prepared by wet chemical methods break through the limitations of traditional vacuum coating processes and have good large-scale production capabilities. Especially in the fields of electrochromic display devices and smart window films, they show broad application prospects.

[0004] Existing literature (Cai X, Xiao X, Sheng G, et al. Effect of pH on the structure andmorphology of W 18 O 49 nanowires and their electrochromic properties[J]. CeramicsInternational, 2022, 48(14): 20791 - 20800.) reported a crystalline-amorphous core-shell structure W 18 O 49 nanowire electrochromic ink prepared by ethylene glycol solvothermal method. In this method, ethylene glycol not only provides a reaction environment as a solvent but also acts as a ligand modifier to promote the dispersion of W 18 O 49 nanowires. However, since ethylene glycol cannot be removed by simple low-temperature annealing, the performance of the prepared electrochromic thin film is negatively affected. Specifically, the response time is slower (the coloring time at 633 nm is 7.9 s, and the fading time is 3.9 s), and the coloring efficiency is lower (32.5 cm at 633 nm)2 / C), and poor cyclic stability (only 84.5% of the initial modulation amplitude is retained after 1000 cycles). In order to solve the problems caused by ethylene glycol ligands, researchers usually use dialysis to remove excess ethylene glycol. Another paper (Yao Y, Zhao Q, Wei W, et al.WO 3 quantum-dots electrochromism[J].Nano Energy,2020,68:104350.) reported a method for preparing WO by ethylene glycol solvothermal method. 3 The method of quantum dot electrochromic ink was followed by the spraying technology to prepare WO 3 Electrochromic film. The film is + or Al 3+ The electrolyte exhibits excellent electrochromic properties, such as high optical contrast (97.8% and 94.1% at 633nm, respectively), fast response time (coloring time is 4.5s and 13.5s, fading time is 4s and 10s), and ultra-long cycle life (optical contrast loss is only 10% after 10,000 and 20,000 cycles at 633nm and no performance degradation). However, the method uses dialysis to remove ethylene glycol ligands, which is complex and time-consuming, significantly reduces production efficiency, increases preparation costs and process complexity, and limits the large-scale and rapid preparation of electrochromic films. Therefore, it is particularly important to develop a method for preparing additive-free electrochromic inks that does not rely on complex processing processes. Summary of the invention

[0005] In view of the above technical problems and the shortcomings in the art, the present invention provides a highly dispersible tungsten oxide (WO 3-x ) ink and its preparation method and application. The preparation method of the present invention is simple in process and convenient in operation. 3-x The ink has excellent dispersibility without additional additives and is suitable for various thin film preparation processes such as inkjet printing, spin coating, and spraying. It has good large-scale production capabilities and shows broad application prospects, especially in the fields of electrochromic display devices and smart windows.

[0006] [1] A method for preparing a highly dispersible tungsten oxide ink, comprising:

[0007] Add concentrated hydrochloric acid with a mass concentration of 36% to 38% (e.g., a molar concentration of 12M, etc.) to a sodium tungstate aqueous solution below 0°C to generate a white flocculent precipitate A;

[0008] At room temperature, the white flocculated precipitate A was repeatedly subjected to the operation of adding deionized water, ultrasonication and centrifugation to obtain the precipitate until the pH of the supernatant after centrifugation was greater than 2.5, thereby obtaining a light yellow precipitate B;

[0009] Ultrasonic dispersion of the light yellow precipitate B in an alcohol solvent, and then performing an alcohol solvent thermal reaction at 160-200° C. for 3-36 hours (e.g., 3 hours, 6 hours, 12 hours, 18 hours, etc.); the alcohol solvent includes one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol;

[0010] After the alcohol solvent thermal reaction is completed, the solid product is added to ethanol and centrifuged and the transparent supernatant is poured out to obtain a blue-gray precipitate C;

[0011] The blue-gray precipitate C is ultrasonically dispersed in deionized water, and then centrifuged and purified to obtain the supernatant to obtain a blue aqueous dispersion, namely the highly dispersible tungsten oxide ink.

[0012] The present invention prepares highly dispersible WO without additives by simple alcohol solvent thermal method. 3-x Electrochromic ink, which uses low-boiling alcohol as solvent and reducing agent to prepare WO 3-x The nanomaterials can be well dispersed in water or water-alcohol mixed solutions without any additional additives. 3-x The material has a small size and a high specific surface area, which can provide more active sites for electrochemical reactions, thereby significantly improving the electrochromic performance of the electrochromic film.

[0013] In the preparation method, the volume ratio of the concentrated hydrochloric acid to the sodium tungstate aqueous solution can be 1:5-10.

[0014] In the preparation method, the concentration of sodium tungstate in the sodium tungstate aqueous solution can be 0.5-2M.

[0015] In the preparation method, the first step of adding deionized water for ultrasonic treatment can be performed, and the added volume of deionized water can be 10 to 20 times the volume of the sodium tungstate aqueous solution.

[0016] In the preparation method, the multiple additions of deionized water and ultrasonic-centrifugal precipitation operations can have an interval of 20 to 40 minutes between two adjacent ultrasonic operations.

[0017] In the preparation method, the time for ultrasonic dispersion of the light yellow precipitate B in the alcohol solvent can be 0.5 to 4 hours.

[0018] In the preparation method, the blue-gray precipitate C can be ultrasonically dispersed in deionized water for 10 to 30 minutes.

[0019] In the preparation method, the rotation speed of the centrifugal purification can be 6000-12000 rpm, such as 10000 rpm, etc., and the time of the centrifugal purification can be 6-12 minutes, such as 10 minutes, etc.

[0020] In the preparation method, the concentration of tungsten oxide in the blue aqueous dispersion can be 5-100 mg / mL.

[0021] The preparation method of the present invention does not require the addition of additional additives (such as ethylene glycol, etc.).

[0022] [2] Highly dispersible tungsten oxide ink prepared according to the preparation method described in [1].

[0023] The highly dispersible tungsten oxide ink of the present invention may not contain any additional additives (such as ethylene glycol, etc.).

[0024] [3] Application of the highly dispersible tungsten oxide ink described in [2] in electrochromism.

[0025] The selection and optimization of specific technical solutions and characteristic means in the application can be referred to the introduction in [4] and [5] below.

[0026] Optionally, the highly dispersible tungsten oxide ink can be used to make an electrochromic film.

[0027] [4] An electrochromic film, the raw material composition of which includes the highly dispersible tungsten oxide ink described in [2].

[0028] The thickness of the electrochromic film may be 100-500 nm.

[0029] The electrochromic film may be used in an aqueous electrolyte and / or an organic electrolyte. The aqueous electrolyte may include H 2 SO 4 、ZnSO 4 、Al 2 (SO 4 ) 3 、ZnCl 2 、KCl、MgCl 2 and AlCl 3 The organic electrolyte may include LiClO 4 / PC, NaClO 4 / PC、Mg(ClO 4 ) 2 / PC, Ca(ClO 4 ) 2 / PC and Al(ClO 4 ) 3 / PC, etc. The electrolyte concentration can be 0.1-2M.

[0030] [5] A method for preparing an electrochromic film, comprising: transferring the highly dispersible tungsten oxide ink described in [2] onto a substrate with or without dilution, and annealing to form the electrochromic film. The transfer method may be a conventional technical means in the art, including but not limited to one or more combinations of spray coating, spin coating, and Czochralski coating.

[0031] Annealing can improve the electrochromic performance of the thin film. The annealing can be performed in air. The annealing temperature can be 100 to 500° C., such as 350° C. The annealing time can be 0.5 to 2 hours.

[0032] The manufacturing method can dilute the highly dispersible tungsten oxide ink and transfer it to the substrate. The dilution multiple can be no more than 10 times. The dilution can be achieved by adding water and / or alcohol to the highly dispersible tungsten oxide ink. Furthermore, the alcohol used for the dilution can include at least one of methanol, ethanol, isopropanol, etc.

[0033] According to the production method, the concentration of tungsten oxide in the highly dispersed tungsten oxide ink transferred to the substrate can be 0.5-10 mg / mL.

[0034] In the manufacturing method, the substrate can be a rigid or flexible substrate, including but not limited to one or more combinations of ITO glass, FTO glass, AZO glass, etc.

[0035] In the manufacturing method, the surface of the substrate is clean and has been treated with plasma and / or ultraviolet (UV).

[0036] In the manufacturing method, the thickness of the electrochromic film can be 100-500nm.

[0037] The performance test of the electrochromic film of the present invention can be carried out by using aqueous electrolyte and / or organic electrolyte. The aqueous electrolyte may include H 2 SO 4 、ZnSO 4 、Al 2 (SO 4 ) 3 、ZnCl 2 、KCl、MgCl 2 and AlCl 3 The organic electrolyte may include LiClO 4 / PC, NaClO 4 / PC、Mg(ClO 4 ) 2 / PC, Ca(ClO4 ) 2 / PC and Al(ClO 4 ) 3 / PC, etc. The electrolyte concentration can be 0.2-2M.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The WO prepared by the simple alcohol solvent thermal method 3-x Nanomaterials can be dispersed in pure water or water-alcohol mixed solvents with high stability without any additional additives, and no precipitation is observed after standing for up to half a year. Secondly, thanks to the excellent dispersibility of the ink, the electrochromic film prepared by spraying has the characteristics of high initial transmittance, large modulation amplitude, fast response time, high coloring efficiency, excellent cycle stability, etc. It has good large-scale production capabilities, and shows broad application prospects, especially in the fields of electrochromic display devices and smart windows. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 (a) X-ray diffraction (XRD) patterns of tungsten oxide of Comparative Example 1, Example 1, Example 2, Example 3 and Example 4, and (b) digital photographs of highly dispersible ink with a concentration of 5 mg / mL using pure water as solvent.

[0042] Figure 2 The high-resolution transmission electron microscope (HRTEM) and selected area electron diffraction pattern photos of Example 1, Example 2, Example 3 and Example 4 are shown.

[0043] Figure 3 For Example 1, the electrochromic film was sprayed with 0.5 MH 2 SO 4 (a) transmittance change curve at different voltages, (b) cyclic voltammetry curve at different scan rates, (c) in-situ transmittance change curve at 633 nm during electrochemical cycling, and (d) coloring efficiency diagram at 633 nm measured for the electrolyte.

[0044] Figure 4 For Example 2, the electrochromic film was sprayed with 0.5 MH 2 SO 4(a) transmittance change curve at different voltages, (b) cyclic voltammetry curve at different scan rates, (c) in-situ transmittance change curve at 633nm during electrochemical cycling, and (d) coloring efficiency diagram at 633nm measured for the electrolyte.

[0045] Figure 5 For Example 3, the electrochromic film was sprayed with 0.5 MH 2 SO 4 (a) transmittance change curve at different voltages, (b) cyclic voltammetry curve at different scan rates, (c) in-situ transmittance change curve at 633nm during electrochemical cycling, and (d) coloring efficiency diagram at 633nm measured for the electrolyte.

[0046] Figure 6 For Example 4, the electrochromic film was sprayed with 0.5 MH 2 SO 4 (a) transmittance change curve at different voltages, (b) cyclic voltammetry curve at different scan rates, (c) in-situ transmittance change curve at 633nm during electrochemical cycling, and (d) coloring efficiency diagram at 633nm measured for the electrolyte.

[0047] Figure 7 The electrochromic film of Example 3 was treated with 0.5 MH 2 SO 4 The in-situ transmittance change curve at 633nm was measured for the electrolyte during 4000 electrochemical cycles. DETAILED DESCRIPTION

[0048] The present invention uses a simple alcohol solvent thermal method to prepare high-dispersion WO without additives. 3-x The ink is coated on the substrate to form a wet film by spraying, spin coating or pulling, and the wet film is annealed in air to obtain WO 3-x Electrochromic film. The present invention is further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0049] Comparative Example 1

[0050] A hydrothermal WO 3 The preparation method comprises the following steps:

[0051] Under ice bath conditions, 5 mL of concentrated hydrochloric acid (12 M) was added dropwise to 30 mL of sodium tungstate dihydrate aqueous solution (0.67 M) to generate a white flocculated precipitate A. 300 mL of deionized water was added to the precipitate A for ultrasonic dispersion at room temperature for 30 min, followed by centrifugation to obtain a precipitate, which was ultrasonically dispersed in deionized water again, and centrifuged continuously. The ultrasonic dispersion and centrifugation operations were repeated until the pH of the supernatant was ≈ 3 to obtain a light yellow precipitate B. This precipitate B was added to 100 mL of deionized water and ultrasonically dispersed for 2 h, then placed in two 100 mL polytetrafluoroethylene reactors and reacted at 180 ° C for 12 h. After the reactor was cooled to room temperature, the solid product was centrifuged and washed with ethanol and water to obtain a yellow precipitate, which could not be well dispersed in water.

[0052] Example 1

[0053] A kind of additive-free highly dispersible WO 3-x The method for preparing ink and electrochromic film comprises the following steps:

[0054] This embodiment uses FTO glass (30mm×30mm) as the substrate, and performs the following cleaning steps before coating: after washing with deionized water for 3 times, the FTO glass is placed in deionized water for ultrasonication for 30 minutes → after washing with ethanol for 3 times, it is placed in ethanol for ultrasonication for 30 minutes → drying at 60°C for 20 minutes → surface plasma treatment for 120 seconds.

[0055] Under ice bath conditions, 5 mL of concentrated hydrochloric acid (12 M) was added dropwise to 30 mL of sodium tungstate dihydrate aqueous solution (0.67 M) to generate a white flocculent precipitate A. 300 mL of deionized water was added to the precipitate A for ultrasonic dispersion at room temperature for 30 min, followed by centrifugation to obtain a precipitate, which was ultrasonically dispersed in deionized water again, and centrifuged continuously. The ultrasonic dispersion and centrifugation operations were repeated until the pH of the supernatant was ≈ 3 to obtain a light yellow precipitate B. After adding this precipitate B to 100 mL of ethanol and ultrasonically dispersed for 2 h, it was placed in two 100 mL polytetrafluoroethylene reactors and subjected to alcohol solvent thermal reaction at 180 ° C for 3 h. After the reactor was cooled to room temperature, the solid product was centrifuged with ethanol, and the supernatant was discarded to obtain a blue-gray precipitate C. Subsequently, the precipitate C was added to 100 mL of deionized water for ultrasonic dispersion for 30 min, centrifuged at 10000 rpm for 10 min, the lower precipitate D was removed, and the supernatant was left to obtain a high concentration of blue WO 3-x Aqueous dispersion. The dispersion was mixed with ethanol in a volume ratio of 1:1 to prepare a spray ink with a concentration of about 2.5 mg / mL. WO was prepared by automatic spraying equipment when the substrate was heated to 100°C. 3-x Finally, WO was prepared by annealing at 350℃ for 30min in air. 3-x Electrochromic film.

[0056] Example 2

[0057] The only difference from Example 1 is that the alcohol solvent thermal reaction time is changed from 3 h to 6 h, and the rest is the same.

[0058] Example 3

[0059] The only difference from Example 1 is that the alcohol solvent thermal reaction time is changed from 3 h to 12 h, and the rest is the same.

[0060] Example 4

[0061] The only difference from Example 1 is that the alcohol solvent thermal reaction time is changed from 3 h to 18 h, and the rest is the same.

[0062] Figure 1 (a) is the XRD spectrum of tungsten oxide of comparative example 1, embodiment 1, embodiment 2, embodiment 3 and embodiment 4. It can be seen from the comparison that comparative example 1 is monoclinic WO 3 , the phases of Examples 1 to 4 are all monoclinic W 18 O 49 , and as the reaction time increases, the crystallinity of the sample improves, the half-width of the (010) characteristic peak narrows and the signal increases. Figure 1 (b) is a digital photo of the highly dispersible ink in each case with water as the solvent concentration of 5 mg / mL. It can be seen from the figure that the ethanol solvothermal sample has good dispersibility. 3 Due to its large size, precipitation occurs after standing for a long time, and the ink dispersion is poor, making it impossible to prepare high-quality electrochromic films.

[0063] Figure 2 The high-resolution transmission electron micrographs and selected area electron diffraction patterns of Examples 1, 2, 3 and 4 are shown in FIG. By comparison, it can be seen that Examples 1 to 4 are all nanorods with a width of about 5 nm, but Example 1 has a shorter reaction time. 3-x There are many defects on the surface of the nanorods, resulting in a low degree of crystallization. Correspondingly, the reaction time of Examples 3 and 4 is longer, the sample has better crystallinity and fewer surface defects, which is consistent with the XRD conclusion.

[0064] Figure 3 , Figure 4 , Figure 5 , Figure 6 The electrochemical and electrochromic performance curves of Examples 1 to 4 are shown in Figure 1. According to the test results, Example 3 has the best electrochromic performance. 3-x Electrochromic film in H +The electrolyte has high initial transmittance (average visible light transmittance>95%), large modulation amplitude (modulation amplitude at 633nm is 90%), fast response time (coloring response time at 633nm is 3.3s; fading response time is 1.6s), and high coloring efficiency (coloring efficiency at 633nm is 81.2cm 2 / C) and other advantages.

[0065] Figure 7 For Example 3, 0.5 MH 2 SO 4 The in-situ transmittance variation curve at 633 nm during 4000 electrochemical cycles was measured for the electrolyte. It can be seen from the figure that after 4000 cycles, Example 3 still retains 76.8% of the initial modulation amplitude, and has excellent cycle stability.

[0066] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing highly dispersible tungsten oxide ink, characterized in that: include: Add concentrated hydrochloric acid with a mass concentration of 36% to 38% to a sodium tungstate aqueous solution below 0°C to generate a white flocculent precipitate A. At room temperature, the white flocculated precipitate A was repeatedly subjected to the operation of adding deionized water, ultrasonication and centrifugation to obtain the precipitate until the pH of the supernatant after centrifugation was greater than 2.5, thereby obtaining a light yellow precipitate B; Ultrasonic dispersion of the light yellow precipitate B in an alcohol solvent, and then thermal reaction of the alcohol solvent at 160-200° C. for 3-36 hours; the alcohol solvent includes one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; After the alcohol solvent thermal reaction is completed, the solid product is added to ethanol and centrifuged and the transparent supernatant is poured out to obtain a blue-gray precipitate C; The blue-gray precipitate C is ultrasonically dispersed in deionized water, and then centrifuged and purified to obtain the supernatant to obtain a blue aqueous dispersion, namely the highly dispersible tungsten oxide ink.

2. The preparation method according to claim 1, characterized in that: The volume ratio of the concentrated hydrochloric acid to the sodium tungstate aqueous solution is 1:5-10; The concentration of sodium tungstate in the sodium tungstate aqueous solution is 0.5-2M; The first step of adding deionized water and ultrasonic treatment is that the volume of the deionized water added is 10 to 20 times the volume of the sodium tungstate aqueous solution; The multiple addition of deionized water and ultrasonic-centrifugal precipitation operations, the interval between two adjacent ultrasonic waves is 20 to 40 minutes; The time for ultrasonic dispersion of the light yellow precipitate B in the alcohol solvent is 0.5 to 4 hours; The blue-gray precipitate C is ultrasonically dispersed in deionized water for 10 to 30 minutes; The rotation speed of the centrifugal purification is 6000-12000rpm, and the time of the centrifugal purification is 6-12min; The concentration of tungsten oxide in the blue aqueous dispersion is 5 to 100 mg / mL; The preparation method does not require any additional additives.

3. Highly dispersible tungsten oxide ink prepared according to the preparation method according to claim 1 or 2.

4. The highly dispersible tungsten oxide ink according to claim 3, characterized in that: The highly dispersible tungsten oxide ink contains no additional additives.

5. Use of the highly dispersible tungsten oxide ink according to claim 3 or 4 in electrochromism.

6. The use according to claim 5, characterized in that: The highly dispersible tungsten oxide ink is used to prepare an electrochromic film.

7. An electrochromic film, characterized in that: The raw material composition of the electrochromic film includes the highly dispersible tungsten oxide ink as described in claim 3 or 4.

8. The electrochromic film according to claim 7, characterized in that: The thickness of the electrochromic film is 100 to 500 nm; The electrochromic film is used in an aqueous electrolyte and / or an organic electrolyte; the aqueous electrolyte includes one or more of H2SO4, ZnSO4, Al2(SO4)3, ZnCl2, KCl, MgCl2 and AlCl3; the organic electrolyte includes one or more of LiClO4 / PC, NaClO4 / PC, Mg(ClO4)2 / PC, Ca(ClO4)2 / PC and Al(ClO4)3 / PC; the electrolyte concentration is 0.1~2M.

9. A method for preparing an electrochromic film, characterized in that: include: The highly dispersible tungsten oxide ink according to claim 3 or 4 is transferred to a substrate with or without dilution, and annealed to form the electrochromic film.

10. The manufacturing method according to claim 9, characterized in that: The dilution multiple does not exceed 10 times; The dilution is achieved by adding water and / or alcohol to the highly dispersible tungsten oxide ink; the alcohol used for the dilution includes at least one of methanol, ethanol, and isopropanol; The concentration of tungsten oxide in the highly dispersed tungsten oxide ink transferred to the substrate is 0.5-10 mg / mL; The transfer method includes one or more combinations of spray coating, spin coating, and Czochralski coating; The substrate is a rigid or flexible substrate, including one or more combinations of ITO glass, FTO glass, and AZO glass; The surface of the substrate is clean and has been treated with plasma and / or UV light; The thickness of the electrochromic film is 100 to 500 nm; The annealing is carried out in air; the annealing temperature is 100-500° C.; and the annealing time is 0.5-2 hours.

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